The invention is based on a method for determining a current angular position of a rotatable magnetic component in an electric drive, and on a device for determining a current angular position of a rotatable magnetic component in an electric drive.
Drives which have a variable rotational speed and are based on synchronous machines constitute the prior art. In order to be able to correctly actuate the synchronous machine, information about the current rotor angle must be available. In this context, the necessary degree of disambiguity is dependent on the number Zp of pole pairs of the motor. The rotor angle must be unambiguously known only within a range of the magnitude 360°/Zp. It is therefore irrelevant whether the angle is x° or x°+(360°/Zp).
The rotor angle is usually measured with the aid of an angle sensor. One known possibility is to use a signal-generator magnet and an AMR angle sensor, i.e. an angle sensor which utilizes an anisotropic magneto-resistive effect. However, as a result it is not possible to measure a rotor angle which is unambiguous in an unlimited angle range from 0 to 360° but rather only a rotor angle which is unambiguous in a limited angle range from 0 to 180°. It is therefore not possible to differentiate between a rotor angle of x° and one of x°+180°. Consequently, such an angle sensor system can be used only for synchronous machines with an even number of pole pairs.
In order to obtain an angle signal which is unambiguous in the unlimited angle range from 0 to 360°, the AMR angle sensor can be combined with two Hall sensors. German laid-open patent application DE 102 48 060 A1 describes, for example, such a magnetic field sensor arrangement for an angle sensor and a method for operating such a sensor arrangement. The described magnetic field sensor arrangement comprises an angle sensor by means of which the current angular position of a rotatable magnetic component can be measured in a predefined angle range. At least two sensor elements, by means of which the current magnetic field direction of the magnetic component can be measured, are assigned to the angle sensor, wherein the sensor elements are arranged with respect to one another in such a way that their axes which characterize the main measuring direction enclose an angle. However, with the described magnetic field sensor arrangement, additional components in the form of sensor elements are necessary.
In addition it is known that the rotor angle can be estimated by measuring electrical variables. For this purpose, two known effects can be utilized. For example, the voltage which is induced in the stator coils of the synchronous machine is dependent on the rotor angle. Furthermore, the inductances of the stator coils can depend on the rotor angle, depending on the design of the synchronous machine.
For example, German laid-open patent application DE 10 2006 004 166 A1 describes a method and a circuit arrangement for estimating the rotor angle of a synchronous machine in a stationary state. In accordance with the described method, three brief voltage pulses are applied to the stator windings of the synchronous machine in various directions. The rotor angle is then determined from the measured increases in current.
Patent AT 397 727 B describes, for example, a method and a circuit arrangement for the sensorless sensing of the rotational angle of a rotor of a synchronous machine. The described method determines the rotor angle by means of voltage pulses, it being assumed that the inductances of the stator coils of the synchronous machine depend on the rotor angle in an approximately sinusoidal shape.
It is therefore in principle possible to dispense with an angle sensor and to estimate the rotor angle. However, these angle-estimating methods require complex calculations, generate noise and are less accurate than if an angle sensor system is used.